Origin of the mid-infrared peaks in the optical conductivity of LaMnO3

Abstract

We calculated the infrared conductivity spectrum of orbitally ordered LaMnO3 in phonon frequency and overtone frequency ranges. We considered orbital exchange, Jahn-Teller electron–phonon coupling, and phonon–phonon coupling. The fundamental excitation of the phonon-coupled orbiton was only Raman active, not infrared active, while its overtone modes were both Raman and infrared active. Our calculations reproduced the small peaks near 1300 cm−1 observed both in Raman scattering and infrared conductivity spectra, as consistent with previous experimental results.